The terms activity and selectivity are generally used to characterize the effectiveness of a catalyst with respect to a given chemical reaction. The rate of the reaction is a function of the activity of the catalyst, which may be expressed as the amount of the reactants which are transformed per unit time and per unit surface area (or weight) of the catalyst. On the other hand, the selectivity of a catalyst expresses the amount of a given desired reaction product which is obtained per unit time, per unit mass of transformed reactants and per unit surface area (or weight) of the catalyst.
As is known, the catalysts which are currently used are in general highly specific in their application, but frequently do not fulfill the present high technical requirements of simultaneously achieving high selectivity as well as high activity.
Since the number and the variety of the chemical reactions which are of technical interest have been rapidly increasing, the field of heterogeneous catalysis now presents numerous highly complex problems related to selectivity and activation, whether thermal or otherwise. A considerable amount of research work has thus become necessary in order to obtain new and more effective catalysts for specific applications.
Relatively high reaction temperatures are generally necessary to ensure satisfactory reaction rates. In exothermal reactions, the equilibrium constant decreases as the reaction temperature increases so that the yield of the reaction decreases accordingly. Hence, it is necessary to achieve a suitable compromise in the choice of the temperature of each exothermal reaction, so that the reaction rate may be made sufficiently high without the equilibrium constant becoming too low to ensure a satisfactory yield of the desired product.
An increase of the reaction temperature is moreover undesirable in many cases where high temperatures may affect the stability of the reaction products, thus leading to decomposition thereof, or may produce undesirable secondary reactions.
A main object of the present invention is to achieve acceleration of various types of chemical reactions while largely obviating the above-mentioned drawbacks and limitations.
Another object of the invention is to allow various chemical reactions to be carried out so as to produce given desired reaction products with a satisfactory yield.
A further object of the invention is to provide means suitable for improving selectivity in the catalysis of different chemical reactions which may lie in a broad range of reaction types.